Multi-Protocol Label Switching (MPLS) enables efficient delivery of a wide variety of differentiated, end-to-end services. MPLS supports delivery of such services using a label switched paths (LSPs). Hundreds or even thousands of LSPs may be provisioned in any given MPLS network.
Telecommunications service providers are seeking low cost, bandwidth efficient, and fault-resilient multicast transport for providing MPLS multicast-based services such as “triple play” (Internet/television/telecommunication) services and broadcast TV services. Currently, multicast services are provided via replication at the network edge (i.e., proximate customer access networks), which causes inefficient usage of network bandwidth.
Efforts to support point to multipoint (P2MP) connections are ongoing. While P2MP will help reduce bandwidth inefficiency in the multicast environment, establishing P2MP connections is not sufficient to ensure fault resilient multicast services. There are additional on going efforts to develop Fast reroute (FRR)-like approaches to P2MP protection, yet, these efforts are still in initial stage.
Three major solutions providing fault-resilient multicast services have been developed by the industry, the standards committees and various academic research.
A first solution provides a pair of link/node disjoint point-to-point connections to each destination node. This approach is used, for example, for supporting VPLS. In this solution, separate traffic flows are sent to each destination, which causes inefficient usage of the network bandwidth.
A second solution uses redundant trees. In this approach, two spanning trees are associated with each multicast source node. The trees are constructed in a manner inducing two disjoint paths between a root node “r” and each destination node. The root node “r” sends the multicast traffic on both trees thus every node get two feeds of the multicast flow. Each destination node selects one of the feeds as a primary and the other as backup. The node listens to the primary feed and in case of failure along its primary path it switches to the backup path. The main drawback of this approach is that each destination node needs to detect a failure on the primary path and use such a detection mechanism to switch to its backup feed. Such detection may require additional mechanisms such as, for example, failure notification messages. Such mechanisms significantly increase the failure recovery time.
A third solution provides a fast reroute approach. This approach is an extension of the point-to-point connection fast reroute (FRR) mechanisms. However, extending the FRR to P2MP connections results in several problems, including (a) the need for sending multiple copies of the same packet on the same link and in the same direction; (b) each node involved in signaling multiple sub-LSPs; (c) high operations and management complexity; and (d) a potential need for a significant bandwidth allocation.